Electromagnetic radiation-based three-dimensional “3D” imaging, such as e.g. white-light interferometry “WLI”, can be used in various applications. For example, bio-imaging in medicine and in many other fields is an established application area of the electromagnetic radiation-based 3D imaging with growth potential both in the academic and commercial settings. Especially, label-free bio-imaging is an emerging and active field that is considered to hold a promise as a way to advance molecular medicine, protein based medicine, and many other fields of medicine. To provide reliable imaging results, a system for electromagnetic radiation-based 3D imaging needs to be calibrated with the aid of a calibration artifact whose thickness profile, i.e. the surface relief, is known with sufficient accuracy. Furthermore, the calibration artifact should have suitable shelf life and desired mechanical and optical properties.
A calibration procedure comprises typically obtaining a calibration imaging result at least partly based on electromagnetic waves received from the calibration artifact, and forming calibration data based on the calibration imaging result and the known thickness profile of the calibration artifact. The calibration data can e.g. be in the form of a lookup table or a correction equation with the aid of which an imaging result can be corrected to correspond to e.g. the surface relief of the imaged sample with sufficient accuracy.
A known way to calibrate electromagnetic radiation-based 3D imaging is based on a calibration artifact that has a hard support core and a soft polymer coating. The hard support core is typically manufactured by machining so as to achieve a desired thickness profile for the hard support core. The soft polymer coating can be made of e.g. SU-8 which is epoxy-based viscous polymer. It can, however, be challenging to control the formation of the soft polymer coating with sufficient accuracy. Furthermore, in some cases, the optical properties of hybrid hard-soft calibration artifacts of the kind described above may not be such as needed.